Black cohosh is a smooth (glabrous) herbaceousperennial plant that produces large, compound leaves from an underground rhizome, reaching a height of 25–60 cm (9.8–23.6 in).[2][3] The basal leaves are up to 1 m (3 ft 3 in) long and broad, forming repeated sets of three leaflets (tripinnately compound) having a coarsely toothed (serrated) margin. The flowers are produced in late spring and early summer on a tall stem, 75–250 cm (30–98 in) tall, forming racemes up to 50 cm (20 in) long. The flowers have no petals or sepals, and consist of tight clusters of 55-110 white, 5–10 mm (0.20–0.39 in) long stamens surrounding a white stigma. The flowers have a distinctly sweet, fetid smell that attracts flies, gnats, and beetles.[2] The fruit is a dry follicle 5–10 mm (0.20–0.39 in) long, with one carpel, containing several seeds.[4]

The plant species has a history of taxonomic uncertainty dating back to Carl Linnaeus, who — on the basis of morphological characteristics of the inflorescence and seeds — had placed the species into the genus Actaea. This designation was later revised by Thomas Nuttall reclassifying the species to the genus Cimicifuga. Nuttall's classification was based solely on the dry follicles produced by black cohosh, which are typical of species in Cimicifuga.[4] However, recent data from morphological and genephylogeny analyses demonstrate that black cohosh is more closely related to species of the genus Actaea than to other Cimicifuga species. This has prompted the revision to Actaea racemosa as originally proposed by Linnaeus.[4] Blue cohosh (Caulophyllum thalictroides), despite its similar common name belongs to another family, the Berberidaceae, and is therefore not closely related to black cohosh.

A. racemosa grows in dependably moist, fairly heavy soil. It bears tall tapering racemes of white midsummer flowers on wiry black-purple stems, whose mildly unpleasant, medicinal smell at close range gives it the common name "Bugbane". The drying seed heads stay handsome in the garden for many weeks. Its deeply cut leaves, burgundy colored in the variety "atropurpurea", add interest to gardens, wherever summer heat and drought do not make it die back, which make it a popular garden perennial. It has gained the Royal Horticultural Society's Award of Garden Merit.[5]

Native Americans used black cohosh to treat gynecological and other disorders, including sore throats, kidney problems, and depression.[3] Following the arrival of European settlers in the U.S. who continued the medicinal usage of black cohosh, the plant appeared in the U.S. Pharmacopoeia in 1830 under the name “black snakeroot”. In 1844 A. racemosa gained popularity when John King, an eclectic physician, used it to treat rheumatism and nervous disorders. Other eclectic physicians of the mid-nineteenth century used black cohosh for a variety of maladies, including endometritis, amenorrhea, dysmenorrhea, menorrhagia, sterility, severe after-birth pains, and for increased breast milk production.[6]

Black cohosh is used today mainly as a dietary supplement marketed to women as remedies for the symptoms of premenstrual tension, menopause and other gynecological problems.[3] Recent meta-analysis of contemporary evidence supports these claims,[1] although the Cochrane Collaboration has concluded that there is insufficient evidence to support its use for menopausal symptoms.[7] Study design and dosage of black cohosh preparations play a role in clinical outcome,[8] and recent investigations with pure compounds found in black cohosh have identified some beneficial effects of these compounds on physiological pathways underlying age-related disorders like osteoporosis.[9]

According to Cancer Research UK: "Doctors are worried that using black cohosh long term may cause thickening of the womb lining. This could lead to an increased risk of womb cancer." They also caution that people with liver problems should not take it as it can damage the liver,[10] although a 2011 meta-analysis of research evidence suggested this concern may be unfounded.[11]

Studies on human subjects who were administered two commercially available black cohosh preparations did not detect estrogenic effects on the breast.[12]

No studies exist on long-term safety of black cohosh use in humans.[13] In a transgenic mouse model of cancer, black cohosh did not increase incidence of primary breast cancer, but increased metastasis of pre-existing breast cancer to the lungs.[14]

Liver damage has been reported in a few individuals using black cohosh,[3] but many women have taken the herb without reporting adverse health effects,[15] and a meta-analysis of several well-controlled clinical trials found no evidence that black cohosh preparations have any adverse effect on liver function.[11] Although evidence for a link between black cohosh and liver damage is not conclusive, Australia has added a warning to the label of all black cohosh-containing products, stating that it may cause harm to the liver in some individuals and should not be used without medical supervision.[16] Other studies conclude that liver damage from use of black cohosh is unlikely,[17] and that the main concern over its safe use is lack of proper authentication of plant materials and adulteration of commercial preparations with other plant species.[18]

Because the vast majority of black cohosh materials are harvested from plants growing in the wild,[3] a recurring concern regarding the safety of black cohosh-containing dietary supplements is mis-identification of plants causing unintentional mixing-in (adulteration) of potentially harmful materials from other plant sources.[3]